In the prior art turret type yarn winder, as shown in FIG. 8, a pair of chucks 1a and 1b are arranged in a winding position M and a waiting position N and, when yarn layers wound on a bobbin held on the chuck 1a reaches a predetermined amount; i.e., a full package has been formed; the positions of both the chucks 1a and 1b are exchanged with each other. In general, the chuck 1a on which the package is held always remains at an initial position, while a pressure roller 27' and a traverse guide 5' are gradually moved away from the chuck as the package is being developed.
In the above conventional turret type winder, there is a drawback in that a structure of the winder becomes complicated and a manufacturing cost thereof is expensive because it needs a mechanism for displacing the pressure roller and the traverse guide relative to the chuck and that for exchanging the winding position and the waiting position with each other when the full package is reached.
In addition, when a plurality of winders of the above type are arranged one above the other in a multistage manner, an installation space necessary therefor becomes larger. That is, as shown in FIG. 9, a horizontal room S is necessary for the individual winder for absorbing the outward displacement of the pressure roller 27' and the traverse guide 5' in accordance with the development of the package size as the increment of the yarn layers wound on the bobbin. In the multistage winder arrangement, it is apparent from the drawing that these horizontal odd rooms S are accumulated to a considerable widthwise length.
To solve the problem caused by the odd room S, one attempt is proposed, for example, in the U.S. Pat. No. 5,029,762, in which a pressure roller is supported by a rocker arm to be movable by a limited distance radially away from the package being formed on a bobbin chuck in a winding position, which movement of the pressure roller in accordance with the development of package is detected by a sensor to rotate a turret disc carrying the bobbin chuck in a bobbin position exchanging direction, so that the pressure roller can be maintained within a limited zone including an initial position as well as a contact pressure applied from the pressure roller becomes substantially constant throughout the package formation. This winder is of a random winding system in which a winding angle (an angle made between a yarn trace forming a yarn layer of the package and a plane perpendicular to the package axis) during the package formation is maintained at constant value. In the random winding system, the aforesaid winding ratio monotonously varies from the initiation to the ending of the package formation, during which it passes a plurality of critical points at which the winding ratio becomes an integer. Since the yarn wound on the adjacent layers on the package surface is arranged in a trace very close to each other when the winding ratio is closer to an integer, there is a risk to cause a so-called "ribbon wind" which must be avoided by any of ribbon breaking means. For example, in the winder disclosed in the above U.S. Patent, this ribbon breaking is carried out by periodically moving a traverse guide away from the pressure roller.
On the other hand, there is another system to be compared with the random winding system; a precision winding system, in which a package formation is carried out while maintaining a winding ratio at a constant value. According to this system, although the problem of ribbon wind can be avoided, there is a different problem in that since the winding angle gradually reduces as the package develops, the package may deform when the same has developed to a larger size to result in a so-called bulge on the lateral sides of the package because the inner yarn layers in the package are liable to be pushed outside from the lateral sides of the package to form a bulge. To avoid such the drawback, it is necessary to gradually decrease a contact pressure applied on the package during the winding operation, which pressure adjustment is far different from that disclosed in the U.S. Patent.
The present inventors have found that a precision winder is more suitable for taking up a sensitive fiber such as carbon fiber or ceramic fiber than a random winding type winder, on the view point of the generation of ribbon wind, and studied to develop the winder of the former type capable of eliminating the prior art drawbacks.